Originally, Eclipso was the first incarnation of the Spirit of Wrath who went rogue. Sealed inside the Heart of Darkness, he could posses those that came into contact with it, most famously Bruce Gordon. In the New 52, Eclipso is said to be Lord Kaala, the evil offspring from House Onyx and House Diamond born during an eclipse granting him vast powers and eventually becoming the tyrant of Gemworld.